Field of the Disclosure
The present disclosure relates to a liquid crystal display device, and more particularly, to a substrate having a means for preventing a mount of an orientation film and a liquid crystal display device including the substrate.
Discussion of the Related Art
Recently, a liquid crystal display (LCD) device has been in the spotlight as a next generation display device having high value added because of its low power consumption and good portability.
An active matrix liquid crystal display (AM-LCD) device, which includes thin film transistors as a switching device for a plurality of pixels, has been widely used due to its high resolution and superiority in displaying moving images.
In general, the LCD device is fabricated through an array substrate process for forming a thin film transistor and a pixel electrode on an array substrate, a color filter substrate process for forming a color filter layer and a common electrode on a color filter substrate and a cell process for forming a liquid crystal layer between the array substrate and a color filter substrate.
FIG. 1 is an exploded perspective view showing a liquid crystal display device according to the related art. In FIG. 1, the liquid crystal display (LCD) device includes an array substrate 10, a color filter substrate 20 and a liquid crystal layer 30 between the array substrate 10 and the color filter substrate 20. The array substrate 10 includes a first substrate 12, a gate line 14 on the first substrate 12, a data line 16 crossing the gate line 14 to define a pixel region P, a thin film transistor (TFT) T connected to the gate line 14 and the data line 16 and a pixel electrode 18 connected to the TFT T.
In addition, the color filter substrate 20 facing the array substrate 10 includes a second substrate 22, a black matrix 25 blocking a non-display area corresponding to the gate line 14, the data line 16 and the TFT T, a color filter layer 26 including red, green and blue color filters 26a, 26b and 26c each corresponding to the pixel region P and a common electrode 28 on an entire surface of the second substrate 22.
Although not shown in FIG. 1, a seal pattern may be formed in a boundary portion between the array substrate 10 and the color filter substrate 20 for preventing leakage of the liquid crystal layer 30. A lower orientation film may be formed between the array substrate 10 and the liquid crystal layer 30 and an upper orientation film may be formed between the color filter substrate 20 and the liquid crystal layer 30 for aligning the liquid crystal layer initially. Further, a polarizing plate may be formed on an outer surface of at least one of the first and second substrates 12 and 22.
A backlight unit may be disposed under the array substrate 10 to supply light. When a gate signal turning on the TFT T is sequentially supplied to the gate line 14, the TFT T is turned on and a data signal supplied to the data line 16 is applied to the pixel electrode 18 through the TFT T. As a result, a vertical electric field is generated between the pixel electrode 18 and the common electrode 28 and liquid crystal molecules in the liquid crystal layer 30 are re-aligned by the vertical electric field, thereby the LCD device displaying images due to transmittance change of the liquid crystal layer 30.
The array substrate 10 is fabricated by forming the gate line 14, the data line 16, the TFT T and the pixel electrode 18 on the first substrate 12 through a depositing step, an exposing step, a developing step and an etching step for a source material. The color filter substrate is fabricated by forming the color filter layer 26 and the common electrode 28 on the second substrate 22. In addition, a liquid crystal panel is fabricated by attaching the array substrate 10 and the color filter substrate 12 with the liquid crystal layer 30 interposed therebetween and the LCD device is completed by attaching a driving circuit to the liquid crystal panel.
Since the LCD device uses an electro-optical effect of the liquid crystal that is determined by anisotropy and arrangement state of the liquid crystal molecules, adjustment of the arrangement state of the liquid crystal molecules influences stabilization in display quality of the LCD device. To obtain a uniform initial arrangement state of the liquid crystal molecules, an orientation process is performed.
In the orientation process, an orientation film is formed on each of the array substrate and the color filter substrate by printing a polymeric material such as polyimide and the orientation film is rubbed with a rubbing cloth along a predetermined direction. As a result, a polymer chain in the orientation film is aligned along the predetermined direction to have a directivity and the liquid crystal molecules have a uniform initial arrangement state due to the orientation film.
When the orientation film is formed to have a non-uniform thickness over a display area in the printing step, the orientation film is deteriorated in the subsequent rubbing step. Accordingly, the orientation film is required to have a uniform thickness.
FIG. 2 is a cross-sectional view showing a printing apparatus of an orientation film according to the related art, and FIG. 3 is a cross-sectional view showing a transferring plate and a substrate in a printing apparatus of an orientation film according to the related art. In FIG. 2, a plate cylinder 51 and a substrate 60 contact each other with a transferring plate 53 interposed therebetween, and a polymeric material is transferred to the substrate 60 by adding a pressure to form an orientation film 63. Since the transferring plate 53 having the polymeric material contacts and is pressurized toward the substrate 60, the polymeric material transferred from the transferring plate 53 to the substrate 60 is spread out toward all directions. Although the orientation film 63 corresponding to a pattern region 54 (of FIG. 3) has a uniform thickness, the orientation film 63 corresponding to an outside of the pattern region 54 has a greater thickness because the orientation film 63 is not pressurized.
In FIG. 3, the orientation film 63 on the substrate 60 includes a starting portion 63a, an ending portion 63b and a central portion 63c. Due to rotation of the plate cylinder 51 (of FIG. 2), the pattern region 54 of the transferring plate 53 starts contacting the substrate 60 to form the starting portion 63a and stop contacting the substrate 60 to form the ending portion 63b. Since the polymeric material is pushed out from the central portion 63c to the starting and ending portions 63a and 63b, a thickness of each of the starting and ending portions 63a and 63b is three or four times as great as a thickness of the central portion 63c. The starting and ending portions 63a and 63b may be referred to as a mount of the orientation film 63.
The mount causes deterioration of the orientation film 63 in a subsequent rubbing step. In addition, since the starting and ending portions of the orientation film 63 have a zigzag line, the ending portion belonging to the non-display area is designed to have a relatively great width. As a result, a bezel region corresponding to the non-display area is enlarged.